1. Field of the Invention
The present general inventive concept relates in general to an image conversion device and method, and more specifically, to an image conversion device and a method to interpolate an input image by utilizing a motion estimation that is adaptive to characteristics of the input image.
2. Description of the Related Art
Cinema films are typically recorded at 24 frames per second. Each frame is instantly stored on film and shot on a screen at one time, producing a progressive image together. On the other hand, TVs have different image processing speeds (or frame rates) that depend on TV transmission systems. For instance, NTSC (National Television System Committee) video runs at 30 frames per second, whereas PAL (Phase Alternation Line) or SECAM (Sequential Couleur Memoire) video runs at 25 frames per second. Since TV broadcast transmits an image using radio waves, a number of scanning lines of each frame ranges several hundreds for photographing and transmission thereof, and the image is displayed through scanning.
In order to show motion pictures more effectively using a limited number of scanning lines, TV uses an interlacing method where a frame is divided into two fields, which are alternately scanned. Therefore, a system that uses the NTSC video processes an image at 60 fields per second, whereas a system that uses the PAL or SECAM video processes an image at 50 fields per second.
On the other hand, when a cinema film is played back on a TV monitor at a TV frame rate, an image on an NTSC television system (which runs at 30 frames per second) will look faster, because the number of frames per second differs in a movie screen and the TV monitor. Therefore, when transmitting the cinema film to the NTSC television system, 60 fields should be obtained from 24 frames per second, namely, 5 fields from 2 frames, to synchronize the two frame rates. In general, a 3:2 pull-down technique is most commonly used for converting 24 frames per second of a motion picture material to 60 fields per second. In the 3:2 pull-down, one film frame is scanned three times and a next frame is scanned twice. On the other hand, when the cinema film is played back on a PAL television system or SECAM television system, 50 fields should be created from 25 frames per second, i.e., 2 fields from each frame. This method is called a 2:2 pull-down, where each film frame is scanned twice.
FIG. 1 is a diagram illustrating a conventional image conversion method.
Referring to FIG. 1, a single frame of a film is composed of a top field with odd lines and a bottom field with even lines. To create 3 fields for cinema film to video conversion, one of the top and bottom fields of each frame is repeated. An input image is an interlaced image, where AT denotes a top field of a frame A, AB denotes a bottom field of the frame A, BT denotes a top field of a frame B, and BB denotes a bottom field of the frame B. Suppose that the input image needs to be converted to a progressive image, and AB is the field that needs to be interpolated. At first, a motion estimation (MEATBT) is performed using neighboring fields AT and BT for the interpolation of AB.
However, if motion of hu T used for the interpolation of AB is large, the interpolation that uses the motion estimation based on top fields of AT and BT causes judder in the interpolated frame A. In particular, a mean value of motion estimations calculated based on AT and BT is closer to a pixel value of BT. Thus, when this motion estimation is used, judder occurs in the interpolated frame A.